The invention concerns a hand power tool with a multi-part, manually operable quick-action chuck for disc shaped tools. These hand power tools are mainly grinding machines. Such a machine is known with a quick-action chuck in accordance with the PCT application DE 87/00577. In the known machine, the disc shaped tools are held on one side against a shoulder of a drive spindle, and on the other side, they are subject to loading from a pressure plate of a chuck. The pressure plate concentrically embraces a threaded part which is axially secured in its position and arranged so that it can be rotated. A hand screw part embraces the pressure plate like a sleeve and, with the pressure plate, forms an annulus in which at least one rolling contact bearing and a drive which couples the hand screw part, the threaded part, and the pressure plate. During screw fixing and tightening of the chuck, the pressure plate is pressed axially against the tool, and the tool is thus pressed against the shoulder on the spindle side. Automatic tightening of the chuck occurs as the hand power tool is switched on. The drive facilitates a transmission with torque increase on tightening. The torque increase will also be effective during slackening of the chuck, by turning the hand screw part, whereby the friction contact between the pressure plate and the tool is cancelled. As soon as this friction contact ceases, the chuck as a whole can be loosened.
A disadvantage of the known hand power tool is a relatively high and uncontrollable chucking power between the pressure plate and the tool due to the automatic chucking during operation of this machine. A further disadvantage is the complicated design of the chuck which is susceptible to faults. Vibrations and dust, in particular, degrade the efficiency of the drive.